RAD51 is a eukaryote gene. The protein encoded by this gene is a member of the RAD51 protein family which assists in repair of DNA double strand breaks. RAD51 family members are homologous to the bacterial RecA, Archaeal RadA and yeast RAD51. The protein is highly conserved in most eukaryotes, from yeast to humans. In humans, RAD51 is a 339-amino acid protein that plays a major role in homologous recombination of DNA during double strand break (DSB) repair. RAD51 catalyzes strand transfer between a broken sequence and its undamaged homologue to allow re-synthesis of the damaged region (see homologous recombination models).
Studies have demonstrated a sensitization to certain DNA damaging therapies associated with cellular defects in proteins that promote HR DNA repair. This sensitization is particularly dramatic for DNA cross-linking chemotherapeutic drugs (30-100 times) and ionizing radiation (3-5 times) (Godthelp et al., “Mammalian Rad51C contributes to DNA cross-link resistance, sister chromatid cohesion and genomic stability,” Nucleic Acids Res., 30:2172-2182, 2002; Tebbs et al., “Correction of chromosomal instability and sensitivity to diverse mutagens by a cloned cDNA of the XRCC3 DNA repair gene,” Proc. Natl. Acad. Sci. USA, 92:6354-6358, 1995; Takata et al., “Chromosome instability and defective recombinational repair in knockout mutants of the five Rad51 paralogs,” Mol. Cell Biol., 21:2858-2866, 2001; Liu et al., “XRCC2 and XRCC3, new human Rad51-family members, promote chromosome stability and protect against DNA cross-links and other damages,” Mol. Cell, 1:783-793, 1998).
Several groups have recently demonstrated that HR can be partially inhibited in order to sensitize cells to DNA damaging therapies. Inhibition of XRCC3 (a RAD51 paralog protein), has been demonstrated using a synthetic peptide corresponding to another paralog protein. This peptide sensitized Chinese Hamster Ovary (CHO) cells to cisplatin and inhibited the formation of sub-nuclear RAD51 foci in response to DNA damage (Connell et al., Cancer Res., 64:3002-3005, 2004). Other researchers have inhibited the expression of the RAD51 protein itself (Russell et al., Cancer Res., 63:7377-7383, 2003; Hansen et al., Int. J. Cancer, 105:472-479, 2003; Ohnishi et al., Biochem. Biophys. Res. Commun., 245:319-324, 1998; Ito et al., J. Gene Med., 7(8):1044-1052, 2005; Collins et al., Nucleic Acids Res., 29:1534-1538, 2001) or blocked its function by over-expressing a dominant negative BRC peptide fragment derived from BRCA2 (Chen et al., J. Biol. Chem., 274:32931-32935, 1999). In view of the connection between increased sensitivity to certain DNA damaging therapies and cellular defects in HR DNA repair-related proteins, there is a need for additional compounds that inhibit RAD51.